The safety of two Bacillus probiotic strains for human use

Probiotics based on Bacillus strains have been increasingly proposed for prophylactic and therapeutic use against several gastro-intestinal diseases. We studied safety for two Bacillus strains included in a popular East European probiotic. Bacillus subtilis strain that was sensitive to all antibiotics listed by the European Food Safety Authority. Bacillus licheniformis strain was resistant to chloramphenicol and clindamycin. Both were non-hemolytic and did not produce Hbl or Nhe enterotoxins. No bceT and cytK toxin genes were found. Study of acute toxicity in BALB/c mice demonstrated no treatment-related deaths. The oral LD₅₀ for both strains was more than 2 × 10 ¹¹ CFU. Chronic toxicity studies were performed on mice, rabbits, and pigs and showed no signs of toxicity or histological changes in either organs or tissues. We demonstrated that while certain risks may exist for the B. licheniformis strain considering antibiotic resistance, B. subtilis strain may be considered as non-pathogenic and safe for human consumption.